1. Field of the Invention
The present invention relates to a charging member, an electrophotographic apparatus and a process cartridge in which the charging member is used.
2. Description of the Related Art
As a charging member used for contact charging, Japanese Patent Application Laid-Open No. 2003-316112 discloses a charging member in which resin particles are contained in the surface of the charging member to form irregularities in order to suppress charging unevenness in a photosensitive member.
The surface of a charging member used for contact charging is gradually contaminated with use by adhesion of substances attributed to a developer, for example, a toner, an external additive, paper powders, etc. This tendency is remarkable particularly in a charging member having irregularities formed on the surface thereof as described above. When using a charging member in which these substances have adhered to its surface is used to form an electrophotographic image, defects in dot or streak form occur in- some cases in the electrophotographic image due to charging unevenness attributed to the contamination. Such defects are observed particularly remarkably in halftone images. Moreover, the defects are liable to occur particularly in a method of applying only direct voltage to a charging member to charge a photosensitive member.
A charging member used for contact charging always contacts a photosensitive member. Therefore, when an electrophotographic apparatus is left standing in a state of rest for a long time, a certain portion of the charging member is in pressure contact with the photosensitive member. As a result, deformation that is not easily restored, i.e., the so-called permanent deformation occurs in some cases in the pressure contacting portion. Hereinafter, such deformation is referred to as “compression set” or “C set”. When a charging member having the C set is used to form an electrophotographic image, striped unevenness occurs in some cases in the electrophotographic image corresponding to the portion where the C set has occurred.